diff -up ./java/org/apache/jasper/compiler/JDTCompiler.java.orig ./java/org/apache/jasper/compiler/JDTCompiler.java 
--- ./java/org/apache/jasper/compiler/JDTCompiler.java.orig	2021-02-03 16:33:37.896971294 +0800
+++ ./java/org/apache/jasper/compiler/JDTCompiler.java	2021-02-03 17:42:27.285007084 +0800
@@ -308,7 +308,7 @@ public class JDTCompiler extends org.apa
             } else if(opt.equals("14")) {
                 settings.put(CompilerOptions.OPTION_Source, CompilerOptions.VERSION_14);
             } else if(opt.equals("15")) {
-                settings.put(CompilerOptions.OPTION_Source, CompilerOptions.VERSION_15);
+                settings.put(CompilerOptions.OPTION_Source, "15");
             } else if(opt.equals("16")) {
                 // Constant not available in latest ECJ version shipped with
                 // Tomcat. May be supported in a snapshot build.
@@ -367,8 +367,8 @@ public class JDTCompiler extends org.apa
                 settings.put(CompilerOptions.OPTION_TargetPlatform, CompilerOptions.VERSION_14);
                 settings.put(CompilerOptions.OPTION_Compliance, CompilerOptions.VERSION_14);
             } else if(opt.equals("15")) {
-                settings.put(CompilerOptions.OPTION_TargetPlatform, CompilerOptions.VERSION_15);
-                settings.put(CompilerOptions.OPTION_Compliance, CompilerOptions.VERSION_15);
+                settings.put(CompilerOptions.OPTION_TargetPlatform, "15");
+                settings.put(CompilerOptions.OPTION_Compliance, "15");
             } else if(opt.equals("16")) {
                 // Constant not available in latest ECJ version shipped with
                 // Tomcat. May be supported in a snapshot build.